Electrolytic pickling apparatus



United States Patent C?" 3,082,164 ELECTRQLYTIC PICKLING APPARATUS Howard R. Palmer, Henderson, Nev., assigner to Titanium Metals Corporation of America, New York, N.Y., a corporation of Delaware Filed Mar. 13, 1961, Ser. No. 95,055 1 Claim. (Cl. 204-225) This invention relates to a pickling apparatus and more particularly to an apparatus useful in a process for electrolytic pickling of a fiat-rolled metal product.

The term flat-rolled metal product as used herein is intended to include metallic plate, sheet, strip and other relatively thin and flat metal products. During the course of manufacture of such products a pickling step is often employed to remove scale which may have been formed as a result of exposure to the atmosphere at elevated temperature and also to remove a surface thickness of metal which may have been contaminated during such processing. A number of different methods are available for pickling metals; however, the general process in which an electrical current is employed to supplement the effect of an acid solution is often used for particular applications, and heretofore has been specifically proposed for metals which under some circumstances are ditlicult to process by ordinary methods, suchpas titanium. In electrolytic pickling, the product being pickled is su-bmerged in an electrolyte which generally comprises an aqueous acid solution and which may optionally contain one or several of a large variety of supplementary salts or compounds. The product is connected electrically to a pole of 4a source of direct electric current, very often the positive, and thus becomes an anode. Another electrode, in this case a cathode, fabricated of metal ormaterial which will not corrode under processing conditions is also submerged in the electrolyte in juxtaposition to the surface of the product from which it is desired to remove scale and contaminated metal. This cathode is, naturally, connected to the negative pole of the electric current source. Electric current is then passed between the submerged cathode and the product acting as an anode, and an eiiicient pickling and metal removing effect can -be obtained. In such a process, however, diiiiculty has heretofore been encountered in-providing a suitable electrical contact with the product to be pickled and this is particularly difficult in the case of a thin sheet or plate having a relatively large flat surface area over which it is desirable to maintain a more or less uniform supply of connected electric power. If connection is made to one corner of a thin sheet, for example, it has been found that remote areas of the sheet are not as eiiiciently pickled due t-o their distance from the electric power connection and poor conductivity of the thin sheet. Additionally it is desirable in such a process to maintain the surface of the product to be pickled in relatively close but nevertheless uniform spaced relation to the juxtaposed cathode surface. Mechanical problems of maintaining a flat product inthe desirable spaced relation to a cathode and also problems of a uniform supply of electric current to the flat product `body have heretofore impeded progress in the electrolytic pickling art.

It is therefore a principal object of this invention to provide an improved pickling apparatus. Another object of this invention is to provide an improved apparatus useful in a process for electrolytic pickling of a flatrolled'metal product. Another object of this invention is to provide apparatus useful in an electrolytic pickling process which provides uniform supplyrof electric current to the product being pickled. Yet another object of this invention is to provide improved apparatus useful in a process for electrolytic pickling in which a hat-rolled product to be pickled is maintained in uniform spaced 3,082,164 Patented Mar. 19, 1963 relation to a juxtaposed electrode. These and `other objects of this invention will be apparent from the following description thereof and from the annexed drawings in which:

FIG. 1 shows a vertical generally central section of a device embodying features of this invention with the upper electrode lowered and adjusted into operating position.

FIG. 2 shows a vertical transverse section on the device of FIG. 1 taken along the line 2 2.

Referring now to FIGS. l and 2, the pickling apparatus comprises an open top rectangular container 10 having side Walls 12 and bottom 14. Projecting inwardly from side walls 12, intermediate the bottom and top thereof, is horizontal shelf 16 which is suitably braced and maintained in rigid position by provision of braces 1S. Shelf 16 is continuous, being iixedly attached to the interior surfaces of side walls 12 and extending completely around the interior of container 10.

A rigid, electrically conductive, perforated and preferably heavy plate 20 is mounted inside container 10, attached at its underside to vertical member 22. Fixedly attached to the base of vertical member 22 is horizontal support member 24 which is of 4such dimension as to cover and overlap the edges of an aperture 26 in the bottom 14 of container 10. Interposed between member `24 and container bottom 14 is a resilient gasket 28, which may suitably be of rubber, and which completely surrounds aperture 26 so `that the bottom 14 is effectively sealed. Projecting from the bottom of member 24 are Ibolts 30 whose shanks pass through locking plate 32 and from which they are electrically insulated by insulating bushings 34, which bushings also insulate plate 32 from auxiliary metal washers B8. Next to washer 38 on one bolt 30 is placed the terminal lug '40 which is tightened in place by locking nut 42, similar nuts 42 also being tightened over washers 38 on the other bolts 30. Terminal lug 40 is in turn `suitably connected, as by connecting wire 44, to a pole of a source of electric current (not shown). It will be seen that perforated plate 20 is thus mounted inside container 10 and means for connecting electric current thereto comprise wire 44, lug 40, bolt 30, support member 24, and vertical member 22.

As will be seen from FIGS. 1 and 2, perforated plate 20 is arranged so that its upper surface is elevated somewhat above the internal edge of shelf 16 on which is disposed resilient gasket 46, which surrounds the internal edges of shelf 16 and also surrounds the outer edge of th upper surface of perforated plate 20.l

A plate is provided to act as an electrode as at 48, and which is mounted so that it may be adjusted into uniform spaced relation to the surface of a flat-rolled product, for example, in the embodiment illustrated, sheet 50, which is maintained, as will be hereinafter described in more detail, in firm contact with the upper surface of perforated plate 20. Such means comprise insulating lblock 52, to the underside of which electrode 48 is firedly attached, as by bolts 54, and which in turn is itself attached as by bolts 56 to bracket arm 58. One end of bracket arm 58 is suitably attached to side wall 12 by a hinged mounting as at 60. Spacer block 62 is of such dimension that when bracket arm 58 is lowered as shown, the electrode 48 will be in adjustment to provide the required uniform spaced relation to the upper surface of .Sheet 5i?. To a convenient point on electrode 4S is attached, as by welding, terminal 64 which is in turn connected by wire 66 to the other pole of the electric currentr source. j

Through -a lower part of wall 12 of container =10 is provided la suitable drain `68 equipped with a valve 72. It will be seen that when sheet 50 is disposed on perforated plate 2t) with its edges in contact with gasket 46, it

together with shelf 16 and gasket 46 divided the container 10 into an upper part and a lower part; the so-divided lower part forming an enclosure about the under surface of sheet 50. Means are provided to evacuate this enclosure or lower part of container 10 which include a nippley 74 passing through side wall 12 of container 10 which is connected through suitable piping 76 to vacuum pump 78. Piping 76 is provided with bleed valve 80 and shut-off valve 82.

Operation of this invention will be described for illustr-ation as used for electrolytic pickling of titanium metal, `although it will be understood that other metals, for example, stainless steel, may be similarly treated if desired.

Bracket arm 58 is first raised to swing upper electrode 48 cle-ar of container 10. A sheet or other at milled product 50, as for example, a scaled sheet of commercially pure titanium, is then placed in position with the outer edges of its under surface in contact with gasket 46. Sheet 50 is pressed down evenly so that it contacts gasket 46 around its entire periphery. This may -be accomplished for example, manually, or may be arranged by placing suitable spacer blocks or bars on sheet G and then lowering electrode 43 in place and pressing down uniformly around the edges of sheet 50a With good continuous contact obtained between the outer edges of sheet 50 and gasket 46, bleed valve 80 is closed, shut-off valve 82 is opened and vacuum pump 78 is operated to evacuate the lower part of container below shelf 16 and which is now enclosed at its top by sheet S), and sealed by `gasket 46. Because of evacuation below, sheet 50 will be forced, by reason of atmospheric pressure on its upper surface, into close mechanical and electrical contact with perforated plate 20. Thus, it will be seen that sheet 50 is flattened in position and also contacted over a major part, or almost all, of its under surface area by plate and maintained in good electrical contact therewith by the vacuum produced underneath it. The vacuum also maintains the seal around sheet S0, effecting compression of gasket 46 by the edges of sheet 50.

With sheet 5% now firmly maintained on the upper surface of electrode 20 and effectively sealed around its outer edges by gasket 46, any pressing blocks employed are removed and electrode 48 is adjusted in suita-ble juxtaposition with its lower surface in uniform spaced relation to the upper surface of sheet 50. Power leads 44 and 66 are now connected preferably to the positive and negative poles respectively of a source of direct electric current. Thus, the sheet 5d becomes an anode and electrode 48 a cathode.

An electrolyte, particularly useful for descaling and pickling titanium, and containing:

Grams per liter Ammonium sulfate 33.0 Potassium dichromate 24.5 Hydrouoric Acid (50% concentration) 30 Balance water.

may be advantageously employed. Such an electrolyte is described and claimed in patent application Serial No. 65,301, filed October 27, 1960, and is particularly effective for removing scale and pickling titanium. A suitable amount of this electrolyte is poured into the upper part of container 10 so as to submerge sheet 5d and at least the lower surface of electrode or cathode 48. Power is then turned on into leads 44- `and 66 to provide between 150 and 250 ani-peres per square foot of the area of sheet 50. Preferably the electrolyte temperature should be to 85 C. for optimum results. Lower temperatures do not alter the effectiveness of the electrolyte but do increase descaling time. After electrolysis for a period of 3 to 5 minutes, depending on the thickness of scale on sheet 5d, the current is switched off, vacuum shut-off valve SZ is closed and bleed valve 8d is opened. When air is bled into the sealed lower portion of container 10 through bleed valve 80, the vacuum lunderneath sheet Si) will be relieved and the sealing effect of gasket 46 around its edges will be lost. Sheet 5d will ordinarily not be perfectly fiat, and with loss of vacuum underneath the sealing effect will also be destroyed. If the seal should not break automatically a corner or edge of sheet 50 may readily be lifted slight to accomplish this. Electrolyte in the upper part of container 1t) will then flow down into the lower part container 10 from whence it may be discharged by opening drain valve 72 and removed to some other convenient storage tank (not shown) through pipe 68.

Bracket 58 is then swung upon its hinge 60 to clear the open top of container 10 and sheet 5t) is removed and rinsed. It will be found to have its top surface descaled and pickled and to have acquired a bright, clean finish. To descale :and pickle the other surf-ace of sheet 5t), it is simply turned upside down, replaced in the apparatus and the operation described above repeated.

It will be obvious to those skilled in the art that various modification and variations in the apparatus design may be made to suit the particular operation and type of metal being treated. For example, the spacing between electrodes Iwill be set for the required electrolytic action. If a large amount of gas is evolved underneath electrode 4S this may be perforated to provide upward venting. The materials of construction will be arranged to counteract the corrosive effect, if any, of the electrolyte employed; if desired the container may be connected to the negative pole of the electric current supply used so that it may be eathodic during electrolysis -and thus be, to an extent, protected from electrolytic corrosion. The dimensions of the electrodes should be adequate to suit their mechanical as well as electrical functions.

A particular advantage of the `apparatus of this invention is that the fiat-rolled product being treated is maintained rigidly on the lower electrode support plate and with excellent electric current distribution over its area. This electric current may be uniformly applied even to a very thin sheet; at the same time the problem of maintaining such a thin sheet in close but uniform spaced relation to la juxtaposed electrode is also solved. It is also a distinct advantage that an efficient electrical connection is made to the sheet to be treated without in any way covering or affecting its surface. Thus, the entire upper surface may be completely pickled and, of course, when turned upside down and the treatment repeated, the entire opposite surface also is treated. In organizations wherein clips, clamps, bolts or other conventional electrical connectors are employed, some part of the sheet surface is inevitably covered, marred or destroyed. This can result in a necessity for clipping of the ends of sheets to remove imperfect sections with corresponding serious production loss.

An important advantage of the apparatus of this invention is that it provides apparatus for efficient electrolytic pickling of sheet or other flat rolled products which are not themselves perfectly Hat. lt will be understood that a sheet of metal may be considerably out of ilat having hills, valleys or oil can liatness irregularity, yet when such a sheet is disposed on a fiat perforated plate surface and vacuum applied underneath atmospheric pressure (amounting to about l ton per square foot), will force the sheet down to correspond in flatness to the perforated plate. Thus, the sheet is maintained in a flatness condition corresponding to the perforated plate and the juxtaposed electrode can be adjusted in precise spaced relation to the sheet surface to be pickled. Thus, the vacuum holding effect achieved in the apparatus of this invention combines three distinct functions; it iattens the sheet, for example, to conform to the surface of the perforated plate, it holds the sheet firmly in position on the perforated plate and it provides excellent electrical contact between the perforated plate and sheet over a large portion or almost all of its area.

Ability to maintain the fiat-rolled product as an anode in uniform spaced relation to a cathode is also important. In electrolytic pickling processes-the amount of metal removed or dissolved is proportional to the amount of electric current used. Therefore, it is necessary to insure that electrolytic action is uniform over the surface area of a sheet or similar product so that the gage removal or reduction in sheet thickness will also be uniform. The cathode to anode spacing affects the electrolytic action and a uniform spacing, readily obtainable with the apparatus of this invention, provides proper electrolytic action and uniform gage removal over the flat-rolled product surface during pickling.

I claim:

Apparatus for electrolytic pickling of a Hat-rolled metal product which comprises:

(1) an open top container;

(2) a continuous shelf projecting inwardly from the side walls of said container intermediate the top andV bottom thereof;

(3) a resilient gasket surrounding the inner edges of said shelf;

(4) a perforated plate mounted in said container having a top surface adapted to support a flat-rolled product whose outer edges contact the said gasket, whereby said flat-rolled product, gasket and shelf divide said container into an upper part and a lowerr Part;

(5) means for evacuating the so divided lower part of said container thereby to provide rm electrical contact and connection between said Hat-rolled product and the top surface of said perforated plate and with the outer edges of said flat-rolled product in sealing engagement with said gasket;

(6) an electrode mounted on said container and adapted to be adjusted into uniform spaced relation to the upper surface of said at-rolled product when maintained on the top surface of said perforated plate by evacuation of said lower part of said container; and,

(7) means for connecting electric current to said perforated plate and said electrode when at least the top surface of said flat-rolled product and the bottom surface of said electrode are submerged in an elec trolyte contained in the upper part of said container.

References Cited in the le of this patent UNITED STATES PATENTS 838,346 Livingston et al Dec. 11, 1906 2,074,221 Holland Mar. 16, 1937 2,074,335 Kelly Mar. 23, 1937 2,172,158 Brislee et al Sept. 5, 1939 2,544,510 Prahl Mar. 6, 1951 2,989,445 Lloyd et al June 20, 1961 2,998,372 Wagner Aug. 29, 1961 

